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The importance of an air gap under lift and slide door frames

MikeB555 | Posted in Energy Efficiency and Durability on

Oddly specific question here:  I’m installing a triple-pane, thermally-broken, Shueco aluminum lift and slide door in a home build.

The installation manual calls for a minimum of a quarter-inch gap under the door frame, i.e., below the sill, that should be caulked on the inside and outside.  Our team has already set the door, and the gap is smaller, at roughly 1/16th of an inch.

We are still working out ways to caulk the door effectively inside and out to stop air movement.

Is this gap size likely to be a problem, either for durability or thermal performance?  It’s obviously a major inconvenience to reset the door, so I’m trying to gauge how serious this situation is.

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Replies

  1. Expert Member
    Michael Maines | | #1

    Fully caulked on the exterior or with gaps?

    1. MikeB555 | | #2

      It will be fully caulked both inside and out.

      1. Expert Member
        Michael Maines | | #3

        I mean do the instructions say to leave gaps on the exterior side? I have not seen their installation instructions; I'm just trying to imagine why they require a 1/4" space and sealant on both sides. The two options that come to mind are that a solid bead on the interior and a gapped bead on the exterior would provide a single air-seal and also allow drainage (assuming there's a sill pan.) If they want both bead to be continuous, it could be to create a dead air space that does the same thing as insulation. If it's the latter, then the only thing you're losing is a bit of thermal performance. Most door manufacturers want continuous support under the sill.

        1. MikeB555 | | #4

          The idea that they want dead air space for insulation purposes is my theory as well, but the manual doesn't specify... I'm seeing a bit of condensation on this sill on the interior with the cold winter days and job site heaters running. I'm just trying to gauge how much this matters in terms of the thermal performance of the door.

          1. Expert Member
            Michael Maines | | #5

            Are the jobsite heaters propane- or diesel-fueled? Those put out a little more than a gallon of water for every gallon of fuel burned.

            Is the sill thermally broken? I'd assume so, but my only experience with Schueco is with their PVC products. Even thermally broken, with a metal sill and no thermal break (such as super-high density foam) under the sill, you will likely have condensation when it's really cold out. That's one reason I try to always use a sill pan that drains to the exterior, even if it contradicts the installation instructions.

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